Study Of Deactivation And Promotion Of Catalyst Employed In Hydrogenation Of Butynediol To 1, 4-butanediol

1,4-butanediol (BDO) has been widely used in the pharmaceutical, textile, military and other fields. With its downstream products PTMEG, PBT and PU elastomer development, the demand for BDO increases sharply in China. Domestic enterprises are building many new production lines for BDO. Based on the price advantage of coal in China, the domestic BDO processes are mainly the Reppe method. Although we have mastered the process for the BDO synthesis, the key process technology—hydrogenation catalyst is still dependent on foreign companies. This greatly hampers the BDO industry in our country. It is of great importance to research and develop the hydrogenation catalyst.Since 2003, our group has carried out the research for the catalyst which has been industrialized now. In order to further improve the catalytic performance of the catalyst, we systematically studied the deactivation mechanism of the catalyst and carried out modification of the catalyst in this paper. This research can provide theoretical guidance for the development of a hydrogenation catalyst having longer lifetime. The main conclusions are:1、The deactivation mechanism of an industrial Ni-M/AlO3 catalyst in the liquid phase hydrogenation of 1,4-butynediol aqueous solution was investigated in a continuously operated fixed bed reactor. The results indicate that the main reasons for the catalyst deactivation within the initial running time are pore blockage and active site coverage due to the deposition of oligomer. The activity can be partially recovered by the method of calcine-reduction. The deactivation of the catalyst in the industrial process was also investigated. The results indicate that, the Al2O3 support transforms into its hydrate boehmite (γ-AlO(OH)), associating with the aggregation of metal Ni, the decrease of BET specific surface area and the reduction of pore volume. The hydration of Al2O3 support is the main reason for the deactivation of the catalyst.2、For the hydration problem of Ni/Al2O3 catalyst under hydrothermal conditions, hydrothermal experiments was designed to systematically investigate the structural and textual evolution of the catalyst. The results show that during the hydration of Al2O3, firstly, the water is physically adsorpt on the support Al2O3, and then the physically adsorpted water was transformed into hydroxyl. finally, the hydrate was crystalized into boehmite. The physical and chemical properties of the catalyst were changed due to the hydration of Al2O3. Thus, the hydration of support Al2O3 should be the main reason for the catalyst deactivation. The key point for prolonging lifetime of the catalyst is to improve the hydrothermal stability of support.3、To improve the hydrothermal stability of support Al2O3, the effects of promoters were studied. The results show that SiO2 is the best promoter. Based on the support modified by SiO2 (SiO2-Al2O3), a novel catalyst preparation method impregnation-deposition method was adopted. Firstly, a nickel salt solution containing urea was impregnated in the promoted support; secondly, the sample was sealed and heated to 90℃. A new nickel phyllosilicates species was formed and deposited in situ on the pore wall during the process, which makes strong Ni-support interaction and high Ni dispersion. The catalyst prepared by this method using SiO2-Al2O3 as support exhibits high activity and hydrothermal stability.4、To further improve the reduction stability of the catalyst, a Carbon-covered alumina (CCA) was investigated. This support is prepared by pyrolysis of sucrose dispersed on aγ-Al2O3 support. The addition of carbon resulted in the changes in the surface properties of the support. When the CCA was used in the supported nickel catalyst, the catalyst showed higher nickel dispersion and mild metal-support interaction and higher activity for the hydrogenation of crude 1,4-butanediol solution.